1. Field of the Invention
The present invention relates to a method of manufacturing an on-demand type multi-nozzle ink jet print head that is mounted in an ink jet printer for industrial and office uses.
2. Description of Related Art
There has been proposed a multi-nozzle ink jet print head that has a number of nozzles arranged with a high density and that employs a piezoelectrlc element to drive each nozzle.
In a conceivable ink jet print head of the piezoelectric type, a pressure chamber in provided to store ink therein. A diaphragm is provided as being exposed to the pressure chamber. A piezoelectric element is attached to the diaphragm. The piezoelectric element repeatedly expands and shrinks, whereby the diaphragm displaces repeatedly. The diaphragm generates a pressure variation in the pressure chamber, thereby allowing an ink droplet to be ejected from the pressure chamber through its orifice.
It is easy to control the displacement of the diaphragm and to change the amount of ink ejected. However, the piezoelectric element can displace the diaphragm only by a small amount in response to a unit amount of electric voltage. It is therefore necessary to make large the surface area of the diaphragm exposed in the pressure chamber. It is impossible to decrease the nozzle pitch to as small a 140 xcexcm. Because the driving frequency depends on the shape of the piezoelectric element, the driving frequency can be increased to 20 kHz or more. The ink jet print head of the piezoelectric type can therefore enhance printing speed.
The conceivable ink jet print head of the piezoelectric type will be described below in greater detail with reference to FIG. 1.
The conceivable multi-nozzle ink-jet print head 200 includes a plurality of nozzle rows which are arranged in a predetermined direction X. In each nozzle row, a plurality of nozzles are arranged in a predetermined direction Y which is perpendicular to the direction X. For each nozzle, the ink-jet print head has a pressure chamber 202 that stores ink and that has an orifice 201 to eject ink droplets onto an image recording medium, such as a sheet of paper (not shown), which is positioned confronting the orifice 201. The ink-jet print head 200 has a manifold 208, in correspondence with each nozzle row, for supplying ink to all the pressure chambers 202 that reside in the nozzle row. Each manifold 208 extends in the predetermined direction Y. Each pressure chamber 202 is in fluid communication, via a corresponding restrictor channel 207, to the corresponding manifold 208. The ink-jet print head 200 has a plurality of piezoelectric elements 204 in one to one correspondence with the plurality of pressure chambers 202. A single diaphragm 203 is connected, via elastic material (silicone adhesive material, for example) 209, to the top surfaces 218 of all the plurality of piezoelectric elements 204. The diaphragm 203 is exposed to each pressure chamber 202 in its surface that is opposed to the surface, where the diaphragm 203 is attached to the top surface 218 of the corresponding piezoelectric element 204.
More specifically, the ink-jet print head 200 has a single base plate (piezoelectric element-fixing plate) 206. The plurality of piezoelectric elements 204 are fixedly mounted on the base plate 206. The piezoelectric elements 204 are arranged in the plurality of nozzle rows. The plurality of nozzle rows are arranged in the predetermined direction X, with each nozzle row extending in the predetermined direction Y. Each piezoelectric element 204 has a pair of external electrodes 214a and 214b at their side surfaces 220a and 220b. A manifold-forming assembly 280 is provided over the piezoelectric elements 204 to provide the manifolds 208.
A single support plate 213 is mounted over both the manifold-forming assembly 280 and the piezoelectric elements 204 in order to reinforce the diaphragm 203. The support plate 213 is formed with a plurality of openings 217a in one to one correspondence with the plurality of piezoelectric elements 204. The diaphragm 203 is mounted over the support plate 213. The diaphragm 203 has a plurality of oscillating areas 230 that are exposed through the corresponding openings 217a to confront the top surfaces 218 of the plurality of piezoelectric elements 204. Substantially the central portions of the oscillating areas 230 are connected via elastic material 209 to the top surfaces 218 of the piezoelectric elements 204.
A restrictor plate 210 is mounted over the diaphragm 203 to provide a restrictor channel 207 for each piezoelectric element 204. A pressure chamber plate 211 is mounted over the restrictor plate 210 to provide a pressure chamber 202 for each piezoelectric element 204. A nozzle plate 212 is mounted over the chamber plate 211 to provide an orifice 201 to each pressure chamber 202.
With the above-described structure, electric signals are repeatedly applied to the external electrodes 214a and 214b of each piezoelectric element 204 via input signal terminals 205a and 205b. As a result, electric potentials repeatedly occur between the external electrodes 214a and 214b, and the piezoelectric element 204 repeatedly expands and shrinks in a direction substantially normal to the surface of the base plate 206. The oscillating area 230 of the diaphragm 203, that is connected to the top surface 218 of the piezoelectric element 4, oscillates in directions near to and away from the orifice 201, thereby producing pressure variations in the pressure chamber 202. Ink droplets are ejected from the pressure chamber 202 via the orifice 201. Thus, the piezoelectric element 204 and the corresponding oscillating area 230 in the diaphragm 203 cooperate to serve as an oscillating system.
It is conceivable that the ink-jet print head 200 halving the above-described structure be manufactured in a manner described below.
A plurality of bar- or rod-shaped original piezoelectric elements (which will be referred to as xe2x80x9cpiezoelectric element barsxe2x80x9d, hereinafter) are first prepared. The number of the piezoelectric element bars is equal to the total number of nozzle rows to be mounted in the print head 200. Each piezoelectric element bar has a top surface 218 and toe pair of slia surfaces 220a and 220b which are provided with the pair of external electrodes 214a and 214b, respectively. Each piezoelectric element bar is cut at their two corners 215a and 215b which are defined between the top surface 218 and the side surfaces 220a and 220b. This corner-cutting operation is required to prevent the external electrodes 214a and 214b from being short-circuited to the diaphragm 203 when the diaphragm 203 is bonded to the top surface 218 and also to ensure sufficient amounts of margin in relative positions between the oscillating areas 230 of the diaphragm 203 and the top surfaces 208 of the piezoelectric elements 204. For example, a grinder is pressed against each corner 215a, 215b of each piezoelectric element 204, thereby beveling the corner 215a, 215b. 
After being subjected to the corner-cutting process, all the piezoelectric element bars are arranged on the base plate 206 in the predetermined direction X so that each piezoelectric element bar extends in the predetermined direction Y. Then, the piezoelectric element bars are bonded to the base plate 206. Each piezoelectric element bar is then subjected to a dicing process, in which each piezoelectric element bar is cut into a plurality of individual piezoelectric elements 204 along the predetermined direction Y. This dicing process is performed using a dicing saw.
Thus, in the above-described conceivable production steps, each piezoeloctric element bar is first cut at their corners 215a and 215b, is attached to the base plate 206, and then is finally diced into the plurality of piezoelectric elements 204.
During these production steps, there are several factors that will possibly reduce the processing precision.
First, because each piezoelectric element bar is made of ceramic, the piezoelectric element bar is sintered during its production process. During the sintering process, the piezoelectric element bar deforms and thermally expands. It is therefore difficult to control the width of the piezoelectric element bar uniformly over its entire length. Variations occur in the width of each piezoelectric element bar.
During the corner-cutting process, variations will also occur in the cut widths of the corners 215a and 215b. In this case, the processing precision will become low. If the piezoelectric element bar having large variations in its corner-cutting width is bonded to the base plate 206, there will occur large amounts of errors in the position where the piezoelectric element bar is attached to the base plate 206.
When the piezoelectric element bar thus fixed to the base plate 206 with large positional errors is divided into the individual piezoelectric elements 204 and assembled with the diaphragm 203, the center of the top surface 218 of each piezoelectric element 204 will possibly shift from the center of a corresponding oscillating area 230 of the diaphragm 203. As a result, the amount of spring modulus, at which the oscillating area 230 of the diaphragm 203 will oscillate, differentiates among respective nozzles. The ink ejecting characteristic will differentiate among respective nozzles. The amounts of ink to be ejected from respective nozzles will therefore change among the respective nozzles.
In view of the problems described above, it is an object of the present invention to provide an improved method of manufacturing an ink jet print head to reduce the variations in the amounts of ink to be ejected from respective nozzles.
In order to attain the above and other objects, the present invention provides a method of manufacturing an ink jet print head which has one or more nozzle rows, each nozzle row including a plurality of nozzles, the ink jet print head having a diaphragm that forms at least a part of a wall defining a pressure chamber storing ink for each nozzle, a wall portion that defines a retaining part of the wall defining the pressure chamber for each nozzle, that defines an ink channel for supplying ink to the pressure chamber, and that defines an orifice for ejecting ink droplets from the pressure chamber, a piezoelectric element, provided for each nozzle, to allow, in response to electric signals, the diaphragm to generate a pressure variation within the corresponding pressure chamber, thereby causing an ink droplet to be ejected from the pressure chamber through the corresponding orifice, and a base plate, on which all the piezoelectric elements, the wall portion, and the diaphragm are mounted, the method comprising the steps of: arranging, while referring to a first reference position that is defined on a base plate, one or more original piezoelectric element bars, in one or more rows, on a surface of the base plate, and bonding the one or more original piezoelectric element bars on the surface of the base plate, the number of the one or more rows corresponding to the number of one or more nozzle rows to be mounted in the ink jet print head, the one or more original piezoelectric element bars being oriented with their lengthwise directions corresponding to an extending direction of each nozzle row and being arranged in their widthwise directions to provide the one or more rows, each row being comprised from at least one original piezoelectric element bar, each original piezoelectric element bar having a top surface for being connected to the diaphragm, a pair of side surfaces, on which a pair of external electrodes being attached, and a bottom surface, at which the subject original piezoelectric element bar is bonded with the base plate; subjecting each original piezoelectric element bar, which is fixed on the base plate, to a corner cutting process by cutting at least one of two corner of the original piezoelectric element bar, while referring to a second reference position that is defined on the base plate, the two corners being defined between its pair of side surfaces and its top surface; and subjecting, after the corner-cutting process, each original piezoelectric element bar, which is fixed to the base plate, to a dividing process by dividing each original piezoelectric element bar, along its lengthwise direction, into a plurality of individual piezoelectric elements, while referring to a third reference position on the base plate, the number of the individual piezoelectric elements corresponding to the number of nozzles to be provided in each row.
The method may further comprise the step of mounting the wall portion and the diaphragm onto the base plate, which is already mounted with the individual piezoelectric elements, while referring to a fourth reference position that is defined on the base plate, and bonding the diaphragm, via an elastic material, to the top surfaces of all the individual piezoelectric elements.
The wall portion may include a support portion reinforcing the diaphragm, the support portion being formed with a plurality of openings for the plurality of nozzles in each nozzle row, the diaphragm being exposed through the plurality of openings, and wherein the mounting and bonding step includes a step of bonding a part of each exposed portion of the diaphragm, via the elastic material, to the top surface of the corresponding individual piezoelectric element mounted on the base plate.
The corner cutting process may be conducted by using a dicing saw, and wherein during the corner cutting process for each original piezoelectric element bar, the dicing saw is moved along the lengthwise direction or the subject original piezoelectric element bar with a distance between the dicing saw and the second reference position being controlled to a corresponding amount, the vertical position of the dicing saw distant from the surface of the base plate being fixed to provide a desired cut depth amount on the corner.
The dividing process may be conducted by using the dicing saw, and wherein during the dividing process, the dicing saw is moved along the widthwise directions of the one or more original piezoelectric element bar and along the surface of the base plate repeatedly, thereby allowing the plurality of individual piezoelectric elements, each having a desired length, to be remained on the base plate.
According to another aspect, the present invention provides a method of manufacturing an int jet print head which has one or more nozzle rows, each nozzle row including a plurality of nozzles, the ink jet print head having a diaphragm that forms at least a part of a wall defining a pressure chamber storing ink for each nozzle, a wall structure that defines an ink channel supplying ink to the pressure chamber for each nozzle, the ink channel including, for each nozzle row, a manifold and a plurality of restrictor channels, the plurality of restrictor channels being in fluid communication with the corresponding manifold and being in fluid communication with the plurality of pressure chambers in the subject nozzle row, each restrictor channel serving as an ink fluid path supplying ink to the corresponding pressure chamber from the corresponding manifold, the wall structure further defining, for each nozzle, an orifice ejecting an ink droplet from the corresponding pressure chamber, a piezoelectric element, provided for each nozzle, to allow, upon application of electric signals, the diaphragm to generate a pressure variation within the corresponding pressure chamber, thereby causing an ink droplet to be ejected from the pressure chamber through the corresponding orifice, the diaphragm being bonded to each piemoelectric element via an elastic material, and a base plate, on which all the piezoelectric elements, the wall structure, and the diaphragm are mounted, the method comprising the steps of: arranging one or more original piezoelectric element bars, in one or more rows, on the base plate and bonding the one or more original piezoelectric element bars to the base plate, the number of the one or more rows corresponding to the number of one or more nozzle rows to be mounted in the ink jet print head, the one or more original piezoelectric element bars being oriented with their lengthwise directions corresponding to an extending direction of each nozzle row and being arranged in their widthwise directions to provide the one or more rows, each original piezoelectric element bar having a top surface for being connected to the diaphragm and a pair of side surfaces, on which a pair of external electrodes being attached; subjecting each original piezoelectric element bar, which is fixed on the base plate, to a corner cutting process by cutting, using a dicing saw, at least one of two corners of the original piezoelectric element bar that are defines by its side surfaces and its top surface, while referring to an arbitrary corner-cut reference position that is defined on the base plate; and subjecting, after the corner-cutting process, each original piezoelectric element bar, which is fixed to the base plate, to a dicing process by dividing each original piezoeloctric element bar, along its lengthwise direction, into a plurality of individual piezoelectric elements, while referring to an arbitrary dividing reference position that is defined on the base plate, the number of the individual piezoelectric elements corresponding to the number of nozzles in each row.
The method may further comprise the step of mounting the wall structure and the diaphragm onto the base plate, which is already mounted with the individual piezoelectric elements, and bonding the diaphragm, via an elastic material, to the top surfaces of all the individual piezoelectric elements.